Envelope structure for electron tubes



"as interelectrode "adjustment means.

place. normally rigidly supported on'the envelope wall,

Patented Mar. 31, 1953 UNITED STATES PATENT OFFICE .ENVELOPE STRUCTURE FOR. ELECTRON TUBES Howard. DJDoolittlaStamford, Conn., assignor to Machlett Laboratories, Incorporated, Spring- .Ndale,.C,orm., a.coriwration .of Connecticut ApplicationjDecemher 4, 1950, Serial No; 199,075

1 14 Claims.

This invention relates to means for adjusting interelectrode spacing in electron tubes of coaxial construction and in particular concerns adjustment means in an envelope wall having a diameter in the order of, or greater than, onehalf inch.

In the prior art, folds or convolutions in metallic envelope walls have been used successfully As opposed to an arrangement employing an inwardly extending fold formedin a reentrant portion of the tube envelope, I have used a radially outward extendingfold formed in the exposed surface of the tube envelope. This construction has proved more accessible and more controllable than the inward extending fold. By axial compression of my convolution, an actual shortening of the axial length of the tube envelope takes Since elements in a vacuum tube are a decrease in wall length between the supports of two electrodes will cause corresponding decrease in interelectrode spacing of those element. To date, such means have been employed to accurately obtain closer spacing between grid and cathode, hence higher transconductance, in inverted lighthouse tubes.

As higher frequency operation is sought, more precise control of the grid-anode spacing assumes importance. It is desirable to control this spacing within small limits in'order to obtain uniformity in U. H. F. capacitance from tube to tube. Without such uniformity, substitution of one .tube for another in any given cavity requires excessive retunin of the cavity to regain the desired resonant circuit. For instance, when used in an amplifier operating at a specific frequency, any change in the capacitance of the tube will require compensation by modifying the circuit constants of the cavity (changin its size) in order that resonance be returned to the desired frequency. Since a major change in tube capacity requires a major cavity adjustment, it is desirable to keep the change in capacity, hence the shift in frequency, as small as possible so that a minimum of retuning will be necessary. If a fold in the tube envelope could be used to obtain precise interelectrode spacing, the readjustment necessary in the cavity circuit would be very minor. But most grid to anode spacing folds would have to be placed on the anode terminal, and it has been shown in the past that folds formed in the envelope in general cannot stand atmospheric pressure if they are about one-half inch or more in diameter, as they would probably have to be in this case.

The factors most influential in the success of folds as adjustment means are the deformability of the metal used (which takes into account the gauge of the metal used) and the area of the fold exposed to atmospheric pressure parallel to the tube axis. Since deformability is a physical property of the metal it is a difficult parameter to change. This is because the kinds of metal possible for use in vacuum tubes, particularly for sealing to the envelope insulation, are limited. Likewise, it is unlikely that the gauge could be increased suiiiciently to adequately decrease deformability since rather standard gauge material is used in electron tubes and heavier material would be cumbersome to form for small tube parts. The area of the fold exposed to axial atmospheric pressure, of course, is dependent upon the envelope diameter at its location.

My invention offers a simple solution to the problem of collapse of large folds. My invention consists of a relatively large fold formed directly in the metal tubing which constitutes a portion of the envelope and within that convolution a ring capable of plastic deformation. Use of some soft metal such as copper for this ring will prevent collapse of the convolution except under sufficient axial pressure of vice-like .jaws to compress and deform the ring. When deformed the desired amount, the ring will still offer resistance to any further compression due to atmospheric pressure.

For a better understanding of my invention reference is made, to the following drawing in which the figure shows-a typicalhigh frequency coaxial tube in axial section.

Referring to the figure the tube shown in axial section has within the vacuum envelope three planar active elements, a cathode is and grid H and an anode surface [2. The cathode I0 is indirectly heated by a heater element which is surrounded by tubular heat shield M attached at one end to the active cathode. The cathode itself is supported by a foil tube 15 which is in turn attached to a tubular member l6 forming an inner ply of the cathode terminal. This is sealed near the tubes end to the outer ply of the cathode terminal which is formed by tubular member H. This terminal also acts as one of the heater terminals and is connected to the heater through lead i8. Axial lead l9 connects the other side of heater to cup terminal as which is within and coaxial with tubular members it and I1. An envelope portion affixed to the oathode terminal is composed of a metallic sleeve 2i sealed to insulating ring 22, which is in turn sealed to axial lead I9. A tubular insulator 23 is 3 also attached to insure separation of the heater terminals.

The grid H is held by support 24 which is rigidly connected by means of tubular member 25 and vitreous insulator 26 to cathode terminal ll. Thus, it may be seen that between the active cathode It and grid I! there is a continuous rigid path formed by the support and terminal members. I have found it convenient to place a small outwardly extending radial fold lid in the surface of tubular terminal member ll. Since the cathode terminal outer and inner ply tubular members It and I! are sealed together near the end of the tube and above the radial fold, axial compression of this fold l'ia will cause a decrease in the inter-electrode spacing between cathode and grid by virtue of the fact that this compression represents a shortening of the axial length of envelope between these two elements.

In similar fashion there is a rigid path between grid l! and the active anode surface E2. The first step in this path is again grid support 24 which is affixed to tubular grid terminal 27. Vitreous ring insulator 29 is sealed to terminal 2'! and insulates it from tubular anode terminal 36, which is sealed to the opposite end of ring 29. Anode terminal 30 may be sealed directly to the anode block 3! or indirectly thereto through reentrant shell member 32. Atop the anode block 3! is the active anode surface it, and through the block is exhaust duct 35, terminated in seal-off tubulation 35.

Somewhere in the anode terminal surface 3% an outwardly extending radial fold 3? similar to fold Ha is formed. Because of its relatively large diameter this fold unsupported is unable to withstand atmospheric pressure. Therefore, I have introduced within the fold a plastically deformable ring 38. When vice-like jaws on opposite sides of the fold surrounding the tube are axially closed upon the fold 37 the ring 38 is permanently deformed. Thus, in compressing the radial fold 3? the axial envelope length between the grid and anode is decreased by virtue of the rigidity of the members forming a path between the grid H and anode surface [2. The ring when compressed will not return to its original shape, but will retain its new shape and thus support the radial fold 37 against collapse.

While the large radial fold described is especially valuable for the grid and interelectrode capacitance adjustment, radial folds of this kind are not restricted to this specific use or location. In fact, they may be employed in any envelope 4 location between any pair of electrode members where axial interelectrode spacing adjustment is desired and where an unsupported radial fold would be unable to withstand atmospheric pressure, or various forms of mechanical shock encountered in the course of using the tube.

I claim:

1. An electron discharge device having an anode and a cathode within a vacuum envelope, said envelope consisting in part of a tubular metallic member having an outwardly extending radial fold the inner surface of which is in continuous communication with the vacuum envelope and a ring of permanently deformable material usable within a vacuum envelope within said fold tending to prevent the collapse thereof under atmospheric pressure or mechanical shock.

2. An electron discharge device having an anode and a cathode within a vacuum envelope, the envelope portion between the anode and its adjacent electrode consisting in part of a tubular metallic member having an outwardly extending radial fold, and a ring of readily deformable metal within said fold tending to prevent the collapse thereof under atmospheric pressure or mechanical shock.

3. An electron discharge device having an anode, a cathode and a grid within a vacuum envelope, the envelope segment between anode and grid consisting in part of a tubular metallic member having an outwardly extending radial fold, and a ring of readily deformable metal REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2, i33,634 Stone Dec. 30, 1947 2,443,237

Gaudenzi et al. June 15, 1948 

